1. Field of the Invention
The present invention relates to a honeycomb structure, and more particularly, it relates to a honeycomb structure for use to purify an exhaust gas emitted from a diesel engine.
2. Background Art
A technology to purify an exhaust gas of a gasoline engine is based on an engine operated at a stoichiometric air-fuel ratio and a technology of a three-way catalyst to simultaneously purify HC, CO and NOx. On the other hand, a diesel engine is operated in oxygen excessive atmosphere, and hence the abovementioned three-way catalyst does not function and NOx cannot be reduced in oxygen excessive atmosphere.
An example of a technology to reduce NOx in oxygen excessive atmosphere is a technology of selective catalytic reduction (SCR). In the selective catalytic reduction (SCR), NOx is reduced by using ammonia as a reducing agent. This technology is developed as a technology to purify an exhaust gas from a stationary emission source such as a power generating plant, and a titania-vanadia based catalyst has been used. Hereinafter, the catalyst for use in the selective catalytic reduction will be referred to as the “SCR catalyst” sometimes. “SCR” is an abbreviation for “Selective Catalytic Reduction”.
The highly effective purification of NOx emitted from the diesel engine is required and hence the technology to purify the exhaust gas from the stationary emission source is investigated to apply to a diesel vehicle. There are developed a technology to load the titania-vanadia based catalyst to a cordierite honeycomb in the same manner as in the three-way catalyst (Patent Document 1) and a technology to form the titania-vanadia based catalyst in the honeycomb structure in the same manner as in the catalyst for the stationary emission source (Patent Document 2).
[Patent Document 1] JP-B-H08-11194
[Patent Document 2] JP-B-2675321